The invention relates to a deflection unit having at least one saddle-shaped coil having coil portions, and winding windows, the coil portions having a front end portion and a rear end portion, at least one of the end portions having a part which has a concave shape between two corners.
The invention also relates to a method of manufacturing a saddle-shaped deflection coil having a front and a rear end, at least one of the front or end portions having a part which has a concave shape between two corners.
EP 0 381 267-A1 describes a method of manufacturing deflection units having coils with a concave part at either a rear or a front flange. The concave part is provided by winding a connection portion of the coil in a convex shape around two corner pins and two auxiliary pins, subsequently removing the auxiliary pins and. pushing the convex part into a concave part of the same shape. The convex and later concave parts are limited by corners, i.e. the parts in which the windings change direction. The position of said corners is determined by the position of the two corner pins during winding.
Providing a deflection unit with a concave part offers the possibility of modulating the fields generated by -the deflection coils in such a manner that a greater flexibility can be achieved to correct certain errors such as raster and convergence.
Although this method provides satisfactory results in many instances, the known method and deflection unit offer only limited possibilities for modification of the field generated by the deflection unit. The shape of the concave part is limited, as will be explained later. Particularly in view of the fact that the display windows of CRTs become increasingly flatter, with a strong insistence to reduce the depth of CRTs, leading to larger deflection angles, an increased flexibility to achieve corrections in the generated field would be advantageous.
To this end, the deflection unit in accordance with the invention is characterized in that the following relation holds for the part having a concave shape:
xcex1 greater than xcex2
where xcex1 is an angle between a line through the two corners of the concave part and inner windings of the concave part, and
xcex2 is an angle between said line and the inner windings at the outer side of a corner.
For the known prior art it holds that xcex1 less than xcex2, as will be explained below. This restriction of angles limits the possibilities of modifying the deflection field, severely decreasing the correcting effects that can be achieved by the concave part.
In deflection units in accordance with the invention, the concave parts are more pronounced, offering more possibilities for correction.
The angle xcex2 is preferably less than 10xc2x0, most preferably approximately 0xc2x0. The parts of the coils on either side of the corner portions are then almost in one line.
The angle xcex1 is preferably more than 20xc2x0. At such angles, the concave part is very pronounced, offering a relatively large modulation of the field.
The method in accordance with the invention is characterized in that, during winding at at least one end portion, the coil is wound around four pins to form a convex part, said four winding pins comprising two stationary and two auxiliary pins, whereafter the two auxiliary pins are removed and two additional auxiliary pins are or have been provided within a winding window determined at least by said four winding pins, and the convex part is pushed inwards into the winding window, against the two additional auxiliary pins, forming two portions extending between the two stationary and the two additional auxiliary pins and a concave part between the two additional auxiliary pins, for which concave part the following relation holds:
xcex1 greater than xcex2
Where xcex1 is an angle between a line through two corners of the concave part and inner windings of the concave part, and
xcex2 is an angle between said line and the inner windings at an outer side of a corner.
Within the concept of the invention, xe2x80x98pinxe2x80x99 is to be interpreted as any object around which the windings of the coil are wound (for winding pins) or against which a winding is pressed (for the two additional auxiliary pins).
In contrast to the known method and deflection unit, in which the convex and concave parts substantially have the same shape, the convex shape is transformed into at least three parts, two straight parts and one concave part, in a deflection unit and method in accordance with the invention. This removes some of the restrictions on the shape of the concave part as known from the prior art.